I created a GPO named "Outlook 2010 settings".
We'll right-click on it (in the Group Policy Management Console - or GPMC) and navigate to the following location:
User Configuration | Policies | Administrative Templates | Microsoft Outlook 2010 | Account Settings | Exchange | Cached Exchange Mode
In the right pane, open the following setting:
"Use Cached Exchange Mode for new and existing Outlook profiles"
And select "Disabled":
The "Help" section informs us that:
I also enabled the following setting one folder above:
"Do not allow an OST file to be created"
So my GPO has the following settings enabled (or disabled...) :
I then apply the GPO to the OU containing my test user and logon to a computer on which they do not have an existing profile.
Note: you may have to adjust the GPO order of application as well, for example:
If we go to the location previously indicated, we see that there is no OAB folder and no .ost file:
Likewise, if we look at the Exchange "Server Settings", we will see that "cached Exchange mode" is grayed out:
However, we can ensure that the OAB is not downloaded with the following setting:
[...] Microsoft Outlook 2010 | Account Settings | Offline Address Book | Offline Address Book: Limit manual OAB downloads
Set the number of manual downloads to 0:
This is the result...
An error message for the user:
And even if the OAB folder is created, no .oab files are downloaded: